The present invention relates to high-bypass gas turbine engines, and more particularly to thrust reversers utilized in high-bypass turbofan engines to provide thrust reversal by diverting air from a fan bypass duct.
FIG. 1 schematically represents a high-bypass turbofan engine 10 of a type known in the art. The engine 10 is schematically represented as including a nacelle 12 and a core engine (module) 14. A fan assembly 16 located in front of the core engine 14 includes a spinner nose 20 projecting forwardly from an array of fan blades 18. The core engine 14 is schematically represented as including a high-pressure compressor 22, a combustor 24, a high-pressure turbine 26 and a low-pressure turbine 28. A large portion of the air that enters the fan assembly 16 is bypassed to the rear of the engine 10 to generate additional engine thrust. The bypassed air passes through an annular-shaped bypass duct 30 between the nacelle 12 and an inner core cowl 36, and exits the duct 30 through a fan exit nozzle 32. The core cowl 36 defines the radially inward boundary of the bypass duct 30, and provides an aft core cowl transition surface to a primary exhaust nozzle 38 that extends aftward from the core engine 14. The nacelle 12 defines the radially outward boundary of the bypass duct 30, and the bypassed fan air flows between bypass duct flow surfaces defined by the nacelle 12 and core cowl 36 before being exhausted through the fan exit nozzle 32.
The nacelle 12 is typically composed of three primary elements that define the external boundaries of the nacelle 12: an inlet assembly 12A, a fan cowl 12B interfacing with an engine fan case that surrounds the fan blades 18, and a thrust reverser assembly 12C located aft of the fan cowl 12B. The thrust reverser assembly 12C comprises three primary components: a translating cowl 34A mounted to the nacelle 12, a cascade 34B schematically represented within the nacelle 12, and blocker doors 34C adapted to be pivotally deployed from stowed positions shown in FIG. 1 as radially inward from the cascade 34B. The inner core cowl 36 of the core engine 14 is also part of the thrust reverser assembly 12C, and the fore end of each blocker door 34C is pivoted into engagement with the inner core cowl 36 when the door 34C is fully deployed. The cascade 34B is a fixed structure of the nacelle 12, whereas the translating cowl 34A is adapted to be translated aft to expose the cascade 34B and deploy the blocker doors 34C into the duct 30 using a link arm 34D, causing bypassed air within the duct 30 to be diverted through the exposed cascade 34B and thereby provide a thrust reversal effect. While two blocker doors 34C are shown in FIG. 1, a plurality of blocker doors 34C are typically circumferentially spaced around the circumference of the nacelle 12.
In a conventional thrust reverser design used in the high bypass turbofan engine 10, the cascade 34B is covered by the stowed blocker doors 34C when the thrust reverser assembly 12C is not in use, that is, during normal in-flight operation of the engine 10. A drawback of this type of conventional construction is that the blocker doors 34C define portions of the fan duct outer flow surfaces, and surface interruptions (gaps and steps) and duct leakage resulting from the doors 34C can increase aerodynamic drag and reduce aerodynamic performance. The link arms 34D associated with the blocker doors 34C protrude into the fan duct flow path to further increase aerodynamic drag and other flow perturbation that can cause aerodynamic or acoustic inefficiencies. In addition, the blocker doors 34C incorporate only limited areas of acoustic treatment as well as create discontinuities in the translating cowl acoustic treatment, and are exposed to damage and wear-inducing conditions during normal engine operation. These aspects of conventional thrust reversers can significantly reduce engine performance, engine noise attenuation, specific fuel consumption, and operational reliability.